XRD98L61_01 Datasheet, PDF (30/38 Pages) Exar Corporation – CCD Image Digitizers with CDS, PGA and 12-Bit A/D

XRD98L61
LINE RATE CLOCKS
CLAMP & CAL are the two line rate clock signals.
There are two modes of operation for these clocks.
CAL & CLAMP Mode
In this mode, the CLAMP signal is used to activate the
DC restore Clamp at the CDS input, and the CAL signal
is used to define the Optical Black pixels to be used for
the Black Level calibration function. Typically the
CLAMP pulse comes during the dummy or optical
black pixels at the beginning of each scan line, and the
CAL pulse comes during the longer string of optical
black pixels at the end of each scan line. CLAMP &
CAL must not be active at the same time.
VS Reject Option (CAL & CLAMP Mode)
In the CAL and CLAMP mode, there is an option to
disconnect the CDS from the input pins during the
Vertical Shift time. To enable this option, write a “1” to
the VSreject bit in the Clock register. To properly define
the Vertical Shift time, you must set the ClampCal bit
properly.
In the typical case, the CCD has a few OB pixels at the
beginning of a line (CLAMP time) and a larger number
of OB pixels at the end of a scan line (CAL time). In this
case set the ClampCal bit = 0. This will define the
Vertical shift time as the time from the end of the CAL
pulse to the beginning of the CLAMP pulse.
If a CCD has more OB pixels at the beginning of a line,
then CAL should be active during these pixels and
CLAMP should be active at the end of the line. In this
case, set the ClampCal bit = 1. This will define the
Vertical shift time as the time from the end of the
CLAMP pulse to the beginning of the CAL pulse.
Active Video
Pixels
CCD
Signal
CAL
(Black Level)
CLAMP
(DC restore)
Vert. Shift Reject
(internal)
End of Line N
OB pixels
t_CAL
Vertical Shift
Start of Line N+1
Dummy &
OB pixels
Active Video pixels
Disconnect CDS from
input pins
t _CLAMP
Figure 20. Line Rate Timing with OneShot=0, VSreject=1 & ClampCal=0
Rev. 2.00
30